Note: Descriptions are shown in the official language in which they were submitted.
CA 02809648 2013-03-15
REFRIGERATION APPARATUS AND METHOD
Field of Invention
This application relates to refrigeration apparatus.
Background of the Invention
In refrigeration systems in which the cooling load involves passing moist air
over a
heat exchanger having a surface temperature below the dew point temperature of
the air,
accumulation of frost on the heat exchanger has been a long-standing problem.
Quite typically, defrosting involves ceasing the flow of chilled coolant to
the heat
exchanger, and passing a heated heat transport medium through the heat
exchanger instead.
Other methods of defrosting may include hot water defrost, electric defrost,
and warm air
defrost. In known systems, the heat transport medium, namely the fluid
selected as the
coolant, is used for both purposes. In the cooling mode, the coolant is taken
from the
receiver on the low pressure side of the equipment. In the heating mode the
same fluid,
heated by whatever means, is passed through the cooling apparatus instead.
Defrost systems
of this general type are shown and described, for example, in US 6,481,231 of
Vogel et al.,
issued November 19, 2002, and in US 4,102,151 of Kramer et al.
Summary of Invention
The following summary may introduce the reader to the more detailed discussion
to
follow. The summary is not intended to, and does not, limit or define the
claims. The
disclosure may disclose, and the claims may claim, more than one invention or
more than
one inventive aspect or features of any such invention.
In an aspect of the invention there is a refrigeration apparatus. The
refrigeration
apparatus has a heat exchanger. The heat exchanger has a first flow path for
an air cooling
load to be chilled; a second flow path defining an evaporator for a
refrigerant fluid; and a
third flow path through which to conduct a defrost fluid. The second and third
flow paths are
segregated from each other whereby refrigerant fluid in the second flow path
is isolated from
defrost fluid in the third flow path.
In a feature of that aspect of the invention, the first flow path is an
ambient air
pressure flow path, the second flow path is a low temperature flow path where
the fluid
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evaporates, and the third flow path is a higher temperature flow path where
the fluid does not
change phase. In a further feature, the refrigerant fluid includes a heat
transfer transport
medium carried in the second flow path at a temperature below 0 C. The
refrigerant fluid is
carried at a pressure of greater than 100 psig. In a still further feature,
the defrost fluid is
carried in the third flow path at a temperature greater than 0 C. The defrost
fluid is carried at
a pressure of less than 100 psig. In another feature, the refrigerant fluid
includes CO2. In
still another feature, the defrost fluid includes a fluid other than CO2. In a
further feature, the
defrost fluid is a liquid, the liquid is a brine that includes glycol.
In still another feature of that aspect, the refrigeration apparatus includes
a cooling
machine. The cooling machine has a work input, a cooling output, and a heat
rejection
output. The cooling machine has a working fluid that is other than CO2. In
still another
feature, the third flow path is operatively connected with a heat rejection
output of the
refrigeration apparatus whereby, in operation, the heat rejection output is
connected to heat
the defrost fluid to be conducted through the third flow path. In yet another
feature, the
refrigeration apparatus has a controller operable selectively to direct
refrigerant fluid to the
heat exchanger during a first time period, and to direct defrost fluid to the
heat exchanger
during a second time period, the second time period is different from the
first time period.
In another feature, the refrigeration fluid is at least predominantly CO2; the
defrost
fluid is a brine that is other than CO2; and the third flow path includes a
portion in which the
defrost fluid is heated by recaptured waste heat rejected from the
refrigeration apparatus. In
still another feature, the heat exchanger is a first heat exchanger. The
refrigeration apparatus
further includes at least a second heat exchanger; and a cooling machine
operable to chill
CO2 and to reject heat. The cooling machine has a working fluid. The working
fluid is at
least predominantly ammonia. There is at least a first receiver reservoir in
which one of (a)
the working fluid, and (b) the CO2 is maintained in liquid phase. There is a
thermal reservoir
in which to store recaptured waste heat rejected by the cooling machine. The
control
apparatus is operable selectively to direct chilled CO2 to any of the heat
exchangers, the
control apparatus also is operable selectively to direct heated defrost fluid
to respective ones
of the heat exchangers at times other than when chilled CO2 is directed
thereto.
In still another feature, the apparatus includes a cooling machine operable to
chill
CO2 and to reject heat. The cooling machine has a working fluid. The working
fluid is at
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least predominantly ammonia. The CO2 is chilled by heat exchange with cold
ammonia, and
the defrost fluid is warmed by heat rejected from hot ammonia.
In another aspect of the invention there is a refrigeration apparatus. It has
a cooling
machine having a work input, a cooling output, and a heat rejection output. A
first heat
exchanger is mounted to extract heat from a first cooling load. The first
cooling load has a
frost point. A first transport apparatus is connected to carry a first heat
transfer transport
medium that has been chilled by the cooling output of the cooling machine to
the first heat
exchanger to cool the cooling load. A second transport apparatus connected to
carry a
second, heated, heat transfer transport medium to the first heat exchanger.
The second
transport apparatus is segregated from the first heat transfer transport
medium whereby the
first and second heat transfer transport media are segregated from each other.
When the first
heat transport medium is directed to the heat exchanger, the heat exchanger is
operable at a
temperature below the frost point of the first cooling load. When the second
heat transport
medium is directed to the heat exchanger, the heat exchanger is operable at a
temperature
above the frost point of the first cooling load.
In a feature of that aspect of the invention, the second transport apparatus
is
connected to receive heat from the heat rejection output. In another feature,
the apparatus
further comprises a thermal storage member connected to receive heat from the
heat rejection
output, and the second transport apparatus is connected to receive heat from
the heat
rejection apparatus that has been stored in the thermal storage member. In
another feature,
the first transport apparatus is a low temperature fluid transport apparatus
operable at a
temperature less than 0 C (or, alternatively, at a pressure of greater than
100 psig), and the
first heat exchanger defines an evaporator for the first heat transfer
transport medium. In a
further feature, the first heat transfer transport medium is CO2. In another
feature, the second
heat transfer transport medium is other than CO2. In a further feature, the
second heat
transfer transport medium is a brine that includes glycol. In another feature,
the cooling
machine has a working fluid other than CO2. In a further feature of that other
feature, the
working fluid of the cooling machine is at least predominantly ammonia. In
still another
feature, the cooling machine is housed in a first location, the first heat
exchanger is housed in
a second location, and the first location is independently ventilated to
external ambient.
In still another feature, the refrigeration apparatus includes a receiver
reservoir for the
working fluid of the cooling machine. In another feature, the apparatus
comprises a receiver
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reservoir for the second heat transfer transport medium. In still another
feature, the first
transport apparatus is a transport apparatus operable at temperatures of less
than 0 C. In
another feature, the second transport apparatus is a high temperature
transport apparatus
having an operating envelope at temperatures greater than 0 C. In yet another
feature, the
apparatus includes at least a second heat exchanger mounted to extract heat
from a second
cooling load, the second cooling load having a frost point. In still yet
another feature, the
apparatus includes an ice-making refrigeration load.
In another aspect of the invention there is a method of defrosting a heat
exchanger.
The heat exchanger has a first flow path for a moist air cooling load to be
chilled; a second
flow path defining an evaporator for a refrigerant fluid; and a third flow
path through which
to conduct a defrost fluid. The second and third flow paths are segregated
from each other
whereby refrigerant fluid in the second flow path is isolated from defrost
fluid in the third
flow path, the method comprising conducting refrigerant fluid to second flow
path in a first
time period, during which frost accumulates on the heat exchanger; and
conducting heated
defrost fluid through the second flow path during a second time period whereby
the
previously accumulated frost diminishes.
In a feature of that aspect, the method includes ceasing flow of the
refrigerant during
flow of the defrost fluid. In a further feature, the method includes using CO2
as the
refrigerant fluid. In another feature, the step of conducting heated defrost
fluid occurs at a
temperature greater than 0 C. In a further feature, the method includes using
a brine as the
defrost fluid, the brine including glycol. In another feature, the method
includes using a
refrigerating apparatus to chill the refrigeration fluid, rejecting heat from
the refrigeration
apparatus while chilling the refrigeration fluid; and using the rejected heat
to heat the defrost
fluid. In a further feature, the method includes saving heat rejected at a
first time, and using
that rejected heat to heat the defrost fluid at a later time. In still another
feature, the method
includes employing ammonia as a working fluid in the refrigeration apparatus.
In yet still
another feature, the method includes using heat rejected from the
refrigeration apparatus also
to address at least one additional heating load other than heating the defrost
fluid. In another
feature, the method includes using refrigerant chilled by the refrigerating
apparatus to
address at least one additional cooling load other than chilling refrigerating
fluid for chilling
the air cooling load of the heat exchanger. In a further feature, there is a
plurality of heat
exchangers having air cooling loads, and the method includes cycling
refrigerant fluid and
defrost fluid to the plurality of heat exchangers selectively whereby each
heat exchanger has
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a defrost cycle. In another feature, the method includes using a refrigeration
apparatus to
chill the refrigeration fluid, and the method includes using CO2 as the
refrigeration fluid.
In another aspect, there is an energy management system. The energy management
system includes a refrigeration apparatus. The refrigeration apparatus is
operable to reject
heat. A heating load apparatus is connected to be heated by the heat rejected
from the
refrigeration apparatus. The heating load apparatus includes a defrost
apparatus. A load
management control system is operable at a first time to cause ice to be made
at the
refrigeration load ice sheet apparatus and to cause heat to be directed from
the refrigeration
apparatus to the defrost apparatus. The load management control system is
operable at a
second time to cause the thermal storage apparatus to be charge as a cold sink
and to cause
heat to be directed from the refrigeration apparatus to the heating load
apparatus.
Brief Description of the Illustrations
These and other features and aspects of the invention may be explained and
understood with the aid of the accompanying illustrations, in which:
Figure 1 shows a schematic representation of an example of a refrigeration
apparatus
embodying principles of the invention;
Figure 2 shows a schematic representation of an alternate example of a
refrigeration
apparatus to that of Figure 1, showing a cascade system; and
Figure 3 shows a schematic of a heat exchanger of the refrigeration apparatus
of
Figure 1
Detailed Description
The description that follows, and the embodiments described therein, are
provided by
way of illustration of an example, or examples, of particular embodiments
incorporating one
or more of the principles, aspects and features of the present invention.
These examples are
provided for the purposes of explanation, and not of limitation, of those
principles, aspects
and features of the invention. In the description, like parts are marked
throughout the
specification and the drawings with the same respective reference numerals.
The scope of the invention herein is defined by the claims. Though the claims
are
supported by the description, they are not limited to any particular example
or embodiment,
and any claim may encompass processes or apparatuses other than the specific
examples
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described below. Other than as indicated in the claims themselves, the claims
are not limited
to apparatuses or processes having all of the features of any one apparatus or
process
described below, or to features common to multiple or all of the apparatus
described below.
It is possible that an apparatus, feature, or process described below is not
an embodiment of
any claimed invention.
The terminology used in this specification is thought to be consistent with
the
customary and ordinary meanings of those terms as they would be understood by
a person of
ordinary skill in the art in North America. The Applicants expressly exclude
all
interpretations that are inconsistent with this specification, and, in
particular, expressly
exclude any interpretation of the claims or the language used in this
specification such as
may be made in the USPTO, or in any other Patent Office, other than those
interpretations for
which express support can be demonstrated in this specification or in
objective evidence of
record, demonstrating how the terms are used and understood by persons of
ordinary skill in
the art, or by way of expert evidence of a person or persons of experience in
the art.
In the discussion herein, a refrigeration machine, or chiller, is one that
draws heat
from a heat source at a lower temperature, and rejects heat to a heat sink at
a higher
temperature. Machines of this nature are sometimes referred to as heat pumps.
In general,
such a machine may be a gas cycle machine or a vapour cycle machine, and will
have a
work input, a cooling load output, and a rejected heat output. The work input
may
correspond to the mechanical work required to drive a compressor (or
compressors) and may
be supplied by an electric or hydraulic motor, or by an internal combustion
engine, or other
suitable power source.
The embodiments of refrigeration apparatus described herein may be vapour
cycle
machines employing a gas phase compressor (or compressors), whether single
stage, multiple
stage or cascade system; a high pressure side condenser whence heat is
rejected from the
working fluid and in which the working fluid changes phase from gas to liquid;
a pressure
reduction device which may be a nozzle or valve; and an evaporative device
such as an
evaporator in which chilled working fluid may absorb heat from air as it is
cooled and in
which the working fluid may "flash", i.e., change phase, from liquid to gas as
it extracts heat
from the heat source to be cooled. Of course, whether a device is a heating or
cooling device
has an aspect of arbitrariness depending on point of view: An evaporator may
be a heating
device for the working fluid, but is equally a cooling device to the cooling
load; the
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condenser is a cooling device for the working fluid, but a heating device for
the medium to
which that heat is rejected.
A distinction is made herein between a primary, or direct, system, in which
the
working fluid passed through the compressor is also the cold side heat
transfer transport
medium circulated through a cooling distribution array; and an indirect system
in which there
is a separate or secondary distribution array, which may employ a heat
transfer transport
medium that is either the same as, or different from, the working fluid of the
primary system
in the refrigeration machine. In an indirect system the working fluid uses as
its heat source a
heat exchanger of the secondary system that forms the heat rejection side of
the distribution
or secondary system.
Where the heat transfer transport fluid of the secondary system is a phase
changing
fluid, the heat source heat exchanger of the primary system may function as
the condenser of
the secondary system, with the distribution array of heat exchangers of the
secondary systems
being the evaporators of the secondary fluid.
Whether the system is a primary, or direct, system, or an indirect system
having a
secondary loop for distribution, where there is a phase changing fluid in
either the primary or
the secondary loop there may be a receiver, or reservoir, in which to collect
a portion of the
heat transport medium, be it primary or secondary. Typically, a receiver may
be located on
the low pressure side, downstream of the condenser and upstream of the
evaporator.
In this specification there is reference to heat transfer transport media. In
general this
term refers to substances that are heated or cooled at one location, and
cooled or heated at a
distant location, thereby transferring heat between the two locations. Most
typically, such
media are fluids. Many fluids have been used as coolants, refrigerants, or
heating fluids.
The fluids may be liquid in one portion of their use in operation, and in gas
form in another
portion of their use or operation. Some fluids are single phase (whether
liquid or gas) or two-
phase (typically liquid and gas). In the refrigeration industry these fluids
are often coolants,
and many of these fluids may be referred to as a "brine" or "brines". A brine
can be a single
phase liquid, and, typically, the term "brine" is used where that liquid has a
freezing point
other than (generally lower than) the freezing point of water. Although
perhaps historically
the term brine may have been derived from a liquid such as water having a salt
in solution
therein, such as to alter its freezing point, the contemporary use of the word
"brine" includes
substances that do not necessarily include dissolved salts such as alcohol,
carbon dioxide
(CO2), ammonia (NH3). The term "volatile brine" is sometimes used to describe
a CO2
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system in which the CO2 does not undergo compression, but is circulated as a
cooling
medium and undergoes a phase change. Brines may also include such things as
glycol (more
properly, ethylene glycol), or partial mixtures of glycol and water. A brine
may also be a two
phase fluid, in which the brine material is at its boiling point, or in which
one component (or
more) of the mixture is in a gas phase, and another is in a liquid phase.
There is also discussion in this specification of "working fluids". In the
context of a
refrigeration system, the "working fluid" is used herein as a fluid in a
primary refrigeration
circuit or system that is compressed in one stage, has heat withdrawn from it
in another stage,
is de-pressurized in a third stage, and has heat added to it in a fourth
stage. Over the last 120
years many fluids have been used as working fluids, including air, Freon
(CFC's), HFC's,
ammonia, and carbon dioxide. There may also be "working fluids" used in
secondary
circuits such as the heat rejection piping array, and in the cooling
distribution array.
Ammonia may be chosen as a working fluid in the refrigeration cycle compressor
for
a number of reasons. It is readily available; it is relatively inexpensive; it
dissipates relatively
quickly and easily in air, it does not tend to cause lasting environmental
damage in terms of
either ozone depletion or greenhouse gas emissions if it leaks, and does not
tend to present a
long lasting toxicity problem when disposal is desired; and, in ice making
technology, there
is a well-established level of knowledge and expertise in the industry in
using ammonia.
Further, the working range of pressures and temperatures for ammonia may tend
to be
suitable for the present purposes. Ammonia may tend to permit the use of
relatively common
oil lubricants, as opposed to highly specialized (and expensive) hygroscopic
oils. Ammonia
may tend to permit smaller pipe sizes, better heat transfer and smaller heat
exchangers. Leaks
may tend to be relatively easy to detect. Ammonia tends to be relatively
tolerant of moisture
in the system.
In the embodiments described, the logic of the system may dictate that the
fluid in a
particular conduit must flow in a particular direction. This may be indicated
in the
illustrations by arrowheads. Although pumps and check valves may be indicated
in the
illustrations, it may be understood that each embodiment is provided with such
circulation
pumps and check valves as may be appropriate to cause fluid to flow in the
correct direction,
without cluttering the illustrations with unnecessary detail. It is also
understood that systems
shown and described herein have suitable pressure relief and surge protection,
as would be
understood by persons of skill without such features being shown.
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Referring to the general arrangement of Figure 1, a refrigeration apparatus is
shown
generally as 20. In general, refrigeration apparatus 20 includes a cooling
machine 22 that has
a work input such as provided at compressors 24, 26 (which may be in parallel,
or may be
staged in series). Refrigeration apparatus 20 also includes one or more heat
rejection outputs,
such as condensers 28; a working-fluid pressure drop apparatus 30, such as a
nozzle or
turbine or motor or work-extracting pump; and a cooling load output 32, such
as at an
evaporator 34. There may be more than one evaporator 34. The cooling load
output 32 can
also be thought of equivalently as a heat input to the system. A receiver or
accumulator, or
reservoir 36 may also be included. Reservoir 36 may be located downstream of
condenser
28, and upstream of evaporator 34. All of items 24, 26, 28, 30, 32 and 34
define elements of
a primary circuit, or loop, or system, of a refrigeration machine such as
cooling machine 22.
Refrigeration apparatus 20 may be located in a building facility, such as may
have a
cooling or refrigeration load, or a variety of such loads, indicated generally
as 40. The
facility may be a factory, such as a food processing factory, but may also be
any other facility
having a refrigeration load. That refrigeration load may include first,
second, third, and
perhaps more, individual heating load members or elements, each of those
cooling loads
being represented generically by a heat exchanger, such as heat exchangers 42,
44 and 46.
Each of heat exchangers 42, 44, 46 may be an evaporator. Each of heat
exchangers 42, 44,
46 is connected to the rest of refrigeration apparatus 20 by a heat transfer
medium transport
apparatus 50, which may have the form of pipes, or piping, or conduits,
however termed, for
carrying the heat transfer transport medium, namely the coolant fluid. It may
be that each of
heat exchangers 42, 44, 46 has its own independent circuit, or flow path of
piping, in a
parallel and independently controllable path, or one or more units may be
arranged in series
depending on cooling loads and needs in the facility.
In the embodiment shown in Figure 1, transport apparatus 50 includes delivery
piping
52 that carries a first heat transfer transport medium, in the form of a
chilled coolant, from a
heat rejection heat exchanger, such as heat exchanger 34, to the refrigeration
or cooling load
or loads 40, and such others as may be, that define a cold sink (or heat
source) at which heat
from loads 40 is added to the coolant, thus raising its enthalpy. Transport
apparatus 50 may
also include return piping 54 that carries higher enthalpy (i.e., heated)
coolant back to heat
exchange 34. As may be understood, the cooling circuit, or loop, that includes
items 42, 44,
46, 50, 52 and 54 is a secondary loop, or secondary system, and it is a
coolant distribution
system or circuit or array, all of which may be indicated generally as 58. The
secondary loop
may include a pump 48, although a pump may not be necessary in all
applications. The
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secondary loop 58 may include a receiver 56. Receiver 56 may define a
reservoir for
condensed coolant, and may be located downstream of heat exchanger 34 (which,
in the
context of secondary loop 58 may act as a condenser), and upstream of such of
heat
exchangers 42, 44, 46 of cooling load 40 as may be.
Similarly, refrigerating apparatus 20 may include a transport apparatus 60,
which may
have the form of pipes, or piping, or conduits, however termed, for carrying a
second heat
transfer transport medium from the heat rejection output of cooling machine 22
to heat
exchangers 42, 44, 46. Transport apparatus 60 may include delivery tubing or
pipes or
conduits, however called, indicated as 62, and return tubing, or pipes, or
conduits however
called, indicated as 64. Transport apparatus 60 may be termed a defrost fluid
transport
apparatus, or circuit, or loop and may have pumps, such as pump 74, control
valves, and
check valves as may be appropriate.
On the heat rejection side, there may be heating loads 66, 68. Whether there
are
heating loads 66, 68 or not, refrigeration apparatus 20 may include a thermal
storage
reservoir 70, which may have the form of a tank 72 in which heated material
may be
retained. As noted, there may be more than one condenser 28. In the embodiment
of Figure
1, there may be a first condenser 76 . Alternatively there may be both a first
condenser 76
and a second condenser 78. First condenser 76 may be connected via piping
manifolds 71
and 73 to thermal storage reservoir 70, and either through manifolds 71 and 73
or through
reservoir 70 to heating loads such as loads 66, 68, or such other heating
loads as the facility
may have, including the defrost load fed by transport apparatus 60. Second
condenser 78 of
apparatus 20 may be an evaporative condenser 78. In the event that either
condenser 76
cannot extract enough heat from the primary working fluid, or in the event
that there is too
much heat stored in thermal storage reservoir 70, that heat can be rejected to
ambient at
second condenser 78. That is, second condenser 78 acts in two modes. In a
first mode, it
exchanges heat from the heat rejection side working fluid to external
atmosphere through one
side or coil, with the return line running in effectively a parallel path back
to receiver 36 as
opposed to coolant passing through condenser 76. In a second mode, second
condenser 78
exchanges heat from the thermal storage reservoir 70 (or from fluid diverted
from manifolds
75) through another side or coil of second condenser 78 to external ambient.
In the second
side or coil it may not be functioning as a condenser, in the sense that the
transport fluid may
be single phase liquid, such as glycol or a glycol mixture, that is not
intended to flash from
liquid to vapour.
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The heated material may be the transport medium to which heat is rejected from
condenser 28. Whether as a decanting tap from thermal storage reservoir 70, a
pipe
connection to hot manifold 71; or as a segregated flow path through a heat
exchange coil
heated by condenser 76 or thermal storage reservoir 70, transport apparatus 60
may be
operated to carry defrost fluid that has been heated by the captured (i.e.,
retained) waste heat
output of machine 22, either directly or in a time-shifted, or time-delayed,
manner from
reservoir 70. The heat transfer transport medium used as the defrost fluid may
be any
suitable fluid. For this purpose, although other fluids might be used in
either liquid or gas
form, the transport fluid may be either polyethylene glycol or a mixture that
is partially
glycol. In the refrigeration loop the transport fluid may be a liquid, and may
remain a liquid
throughout passage through the defrost loop.
In the embodiment of Figure 1, at least one of the refrigerating loads faced
by heat
exchanger 42, 44 or 46 is a moist air cooling load. The nature of
refrigeration is such that the
possibility of frosting is expected where the desired temperature of the
materials to be cooled
at the output cooling load end is to be below the freezing temperature of
water. To that end,
any or all of heat exchangers 42, 44, 46 may be used to chill air in a zone to
be maintained
below freezing; frost may accumulate on the air flow path side of the heat
exchanger. From
time to time, it may be necessary to remove the frost build-up in a defrosting
cycle. In this
discussion, "moist" means that the airflow has high enough absolute humidity
for frost to
form on a below-freezing temperature surface.
In the embodiments shown and described, any or all of heat exchangers 42, 44
and 46
may have three flow passages, or pathways, or coils, or circuits, however they
may be called.
There is a first flow path 80, a second flow path 82, and a third flow path
84.
First flow path 80 may be understood to be the flow path of the fluid of the
cooling
load, namely a moist air flow path. As may be understood, air may be urged
along the flow
path by a blower or fan 85 in a forced air system.
Second flow path 82 may be understood to be the flow path of the refrigerant.
This
flow path may include a finned conduit 86 for the cooling medium. In one
embodiment the
coolant is a substance that is a liquid which may be converted to a gas at
operating pressures,
and that is carried under pressure. Finned conduit 86 may be an evaporator for
that cooling
medium. The cooling medium may be CO2. Finned conduit 86 (and the rest of the
circuit of
which it is part), may have the physical property of being capable of
containing fluids at high
pressure. For the purpose of this description, high pressure is a pressure in
excess of 250
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psia. For CO2 operation, although under various operating conditions the
pressures may be
higher or lower, the piping of the refrigerant flow path may have the physical
property of
being operable not only in excess of 500 psia, but also in excess of 1000
psia, and possibly of
operation at 2000 psia. In normal refrigerating operation, the refrigerant
flows through the
finned tube, and the moist air to be cooled flows through the fin-work, with
heat flowing
from the load to be cooled and into the coolant, reducing the enthalpy of the
load and
increasing the enthalpy of the coolant, possibly to such an extent as may
cause the coolant to
boil in whole or in part.
Third flow path 84 is a defrost flow path. It may include a finned coil 88.
Finned
coil 88 may be parallel to finned coil 86, or it may share the same finwork as
finned coil 86,
or it may be immediately upstream of finned coil 86. Finned coil 86 may share
the same fins
or finwork as finned coil 88. Finned coil 88 and the other components of the
defrost circuit,
define a low pressure circuit or system, which has the physical property of
being operable up
to 250 psia. It may be that the components will contain fluid at higher
pressures, however
the operating range may be less than 100 psig, and may be less than 50 psia.
It may be of the
order of less than 10 psig.
Third flow path 84 is segregated from second flow path 82. That is, the flow
paths of
the refrigerating and defrost circuits are segregated such that coolant from
second flow path
82 is prevented from entering third flow path 84, and coolant from third flow
path 84 is
prevented from entering second flow path, such that neither fluid can
contaminate the other.
Similarly, air from first flow path 80 cannot enter either second flow path 82
or third flow
path 84. In normal operation, second flow path 82 operates at a lesser
pressure than the third
flow path 84. In normal operation both second flow path 82 and third flow path
84 operate at
pressures greater than first flow path 80.
To that end refrigeration apparatus 20 has a controller, which may be an
electronic
controller, and which may be a programmed digital electronic controller. The
controller is
operable to direct chilled coolant through second flow path 82 during normal
refrigerating
operation. The controller is also operable to direct heated defrost fluid
through third flow
path 84. The controller is also operable to cease flow of chilled coolant
during a defrost
cycle and to cease flow of defrost fluid during a refrigeration cycle.
In a system with multiple cooling loads, such as 42, 44 and 46 (or however
many
more loads there may be) the controller is operable selectively to cycle the
chilled coolant
and defrost flows for each unit by causing valves to open an closed
appropriately. That is,
CA 02809648 2013-03-15
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during a defrost cycle one cooling unit may be taken off-line at a time for
defrost, while the
remainder continue to chill the cooling load. When defrost is complete on that
unit, it may
be brought back on-line, and the next unit taken off-line and heated by
defrost fluid, and so
on in turn. Furthermore, where a rejected heat thermal energy storage
reservoir 70 is
employed, heat rejected during a chilling cycle may be retained and used to
defrost the same
heat exchanger previously chilled. It is not necessary that the compressors be
run constantly.
That is, there may be time periods where neither chilling nor defrosting is
required, and the
compressors may be off or dormant. Alternatively, there may be periods where
chilling is
required, but that cooling demand can be met, if temporarily, by the quantity
of chilled
coolant previously accumulated in the receiver, whether in the cooling machine
or in the
coolant fluid distribution array, as may be. Similarly, the defrost fluid pump
74 may be
operated to circulate heated defrost fluid whether the compressors are in
operation or not.
When operated in this manner, the refrigeration system also permits heating
load-shifting
from one time of day to another.
It may be that refrigeration apparatus 20 is part of a larger facility or
building 90.
Referring to the general arrangement of Figure 1, a facility such as a meat or
fish packing
plant 92 may include a zone to be chilled by heat exchangers 42, 44, 46, etc.,
and may also
include other facilities such as a heated water tank, offices or meeting
rooms, change rooms
and showers, and so on. The refrigeration equipment may be fully integrated
with building
mechanical systems in a combined heating, air conditioning and refrigeration
system. It may
be advantageous to employ the rejected heat for additional purposes. It may be
advantageous
to employ the refrigeration apparatus as a heat pump to provide a source of
heat for rejection,
with an ice by-product that can be melted at a subsequent opportunity at which
heat is
required. That is, heating and cooling loads may not occur during the same
time period, or
may be unequally matched. Given that both heating and cooling loads may vary
during the
day, it may be advantageous to provide a large amount of rejected heat at one
time of day,
and a large amount of refrigeration at another.
The building may include a meat or fish packing plant 92, a hot water tank 94,
offices, conference rooms, or meeting rooms 96, change rooms 98, showering
facilities 100,
or some combination thereof The packing plant may include an ice builder 102,
i.e., a
facility designed to cool ice into blocks or cubes, such as may be used, for
example, in the
food service industry or grocery stores, or within the plant itself Such a
building may have
cooling loads (that is, a need for cooling or refrigeration) and heating loads
(that is, a need
CA 02809648 2013-03-15
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for heating) that may vary with the time of day, the season of the year, the
activities
occurring in the building, and the amount of sunshine per day. There may be
simultaneous
heating and cooling loads, as when there is a cooling load to make ice, and a
heating load to
keep the occupied office or meeting spaces wain!. A space that requires
heating at one time
of day may require cooling at another time of day.
In general, there will be time varying-cooling and heating load profiles for
building
90. The cooling load may tend to be lowest at night, and higher during the
day, particularly
when the Sun is shining. During the night the facility may be on "night set-
back", since the
packing facilities may be closed for the night, and need only be maintained in
its condition.
The heat loads may be less at night as well, given the generally cooler
external ambient at
night, the absence of a lighting load (assuming the lights are turned off at
night).
Building 90 may be equipped with an energy management system, indicated
generally as 110, for responding to these environmental loading conditions.
Energy
management system 110 may include refrigeration apparatus 20, as described
above; a cold
sink thermal storage member, or apparatus, indicated as "ice builder" 102; a
hot water supply
104, such as may be used to provide domestic hot water within the plant for
whatever uses; a
building fan coil heating or air conditioning system 106, a building heat pump
108, and a
supplemental heating device 112, such as may be a back-up oil or gas fired
boiler.
Cooling machine 22 of refrigerating apparatus 20 may be contained in a
separate
building, or segregated structure, from the building or structure in which the
coolant
distribution apparatus of items 40 and 50 are located. This construction
permits all devices
through which the primary system working fluid passes (which may be referred
to as the
refrigeration plant) to be segregated from, and to be separately ventilated
from, the enclosed
building structure of the facility in which persons may be at work. In this
way, a leak of the
working fluid may tend not to migrate into occupied areas of the facility, and
may be vented
to external ambient.
The coolant delivery apparatus, or array, so defined by items 40 and 50 may be
quite
large in physical extent. In such a system use of a two phased, or phase
changing, transport
system may permit a large enthalpy change per unit mass of the distribution
fluid, and a
corresponding reduction in both the mass flow rate of that fluid, and of the
pumping power
requirement. The inventor considers CO2 to be a suitable distribution array
heat transfer
CA 02809648 2013-03-15
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transport fluid. At normal operating temperatures between, for example -40C
and +200C,
however, CO2 may be maintained under quite high pressures. Those pressures may
be well
in excess of 250 psia (1.75 MPa), and may typically be higher than 500 psia. A
typical
operating regime may be in the order or 900 ¨ 1200 psia. High pressure piping
may be used,
that piping having the physical property of being operable at those pressures,
and possibly at
much higher pressures in the range of 2000 ¨ 3000 psia. The high pressure
piping may be
steel piping, and may be stainless steel piping. In operation, at very cold (-
40 F) refrigerating
conditions the CO2 may be at about 130 psia. In general operation, the CO2
pressure may be
substantially higher. This may be contrasted with a low pressure liquid piping
system, such
as may carry glycol, which may typically operate at 10 psig. Thus it is
expected that the
waste-heat defrost line will operate at less than 100 psig., whereas the high
pressure
evaporator side will operate at substantially higher pressures than 100 psig,
typically greater
than 120 psia, and almost always at greater than 130 psia. It follows that to
require
defrosting, there must be cooling below 32 F or 0 C in the evaporator or high
pressure path.
Similarly, to defrost, the low pressure defrost fluid must be warmer than 32 F
or C.
In keeping with this, heat transfer transport medium conduit assemblies,
namely the
heating and cooling circuits emanating from segregated structure, such as low
pressure
defrost circuit piping of apparatus 60 that carry defrost fluid to and from
heat exchangers 42,
44, 46, may tend to be relatively low pressure conduits operating at modest
positive pressure
over ambient, carrying a more-or-less non-corrosive liquid heat transfer
medium in the nature
of a liquid coolant of relatively low toxicity, and low volatility, and such
as may tend not to
pose an undue environmental hazard if a leak should occur, such an antifreeze
or antifreeze
mixture, of which one type may be glycol or may include glycol as a component
of a
mixture. Further, when used in the context of this application the term
"glycol" may refer to a
mixture of glycol and water such as may be suitable for the operating range of
the equipment,
be it -30 C to +60 C, -40 C to +70 C or some other range. The pressure of the
defrost piping
may be less than 200 psia, less than 100 psig, may be less than 50 psig (or 50
psia, as may
be), and may typically be of the order of 10 psig. In the inventor's view it
is desirable to
keep the high pressure coolant circuit segregated from the low pressure
defrosting circuit
such that, for example, defrost fluid does not contaminate the coolant system.
Optional ice builder 102 defines a cold sink thermal storage member, or
thermal
capacitance member may, for brevity and simplicity be referred to as an "ice
reservoir". It
may be that the ice reservoir is an accumulation of ice, typically enclosed in
an insulated wall
CA 02809648 2013-03-15
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structure, or tank. It may also be that it is not "ice" at all, but rather a
brine, or an eutectic
fluid, or some other medium such as may tend to have a significant thermal
mass, such that
the ice reservoir may tend to work as a thermal capacitance that can be
"charged up" by being
cooled over a period of time, so that it may then have a large capacity to
cool other objects at
a later time. It may be that the ice reservoir employs a phase change
material, such as a
eutectic fluid as noted above, where there is a significant enthalpy drop
between the warm
state, possibly a liquid state, and the cool, or cold state, possibly a solid
or quasi-solid state.
A liquid freezing point would, for example, tend to be just such a large
enthalpy, narrow
temperature range phenomenon. Where an eutectic material is used, it may be an
eutectic
having a phase change temperature lying in the range of -40 to +20 F, or
possibly in the
narrower range of -20 F to +0 F. The phase change medium may be water, or an
aqueous
solution.
The arrangement described may tend to permit coolant to flow selectively to
either
ice builder 102 or to the elements of cooling loads 40, such as evaporators
42, 44, 46, or to
both in parallel depending on valve positions in the system. Ice builder 102
may be a large
insulated enclosure, or box, or fluid-tight chamber through which liquid
coolant can be
pumped. The enclosure may contain a large number of thermal storage elements
such as steel
coils. They may be stacked to permit interstitial flow of the liquid coolant,
and segregate the
heat transfer storage medium phase change material from the heat transfer
transport medium.
Ice builder 102 has an inlet, and an outlet, such that coolant fed in at the
inlet may tend to
work its way through any of a large number of possible flow paths by wending
about the
collection, or stacked array, to the outlet, this process being accompanied by
heat transfer
between the diffusely moving liquid and the thermal storage medium.
Thermal storage reservoir 70 is a large heat exchange fluid heat transfer
medium
stratification reservoir, or tank. The cold side loop drawing hot coolant from
the outlet of
condenser 76 is carried to the hot side inlet near the top of reservoir 70,
and may be drawn
out at the relatively lower temperature the outlet located near the bottom of
reservoir 70,
through such pumps as may be used, and back to the inlet of evaporator 34.
Thermal storage reservoir 70 is a reservoir in which the rejected-heat side
heat
transfer fluid transport medium may settle and stratify according to
temperature. Thus hot
return flow from condenser 76 is added to the top of thermal storage reservoir
70, and cooled
coolant directed to the inlet of condenser 76 is drawn from the bottom of
thermal storage
CA 02809648 2013-03-15
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reservoir 70. Similarly, hot fluid for direction to the various heating loads
is drawn from the
upper region of storage reservoir 70, and returned to the bottom.
On occasions where there may not be sufficient rejected heat available from
condenser 76 to meet all of the heating loads of the facility 20, or where the
temperature of
the heat rejected is not fully sufficient to meet the temperature requirements
of, for example,
a radiant or fan coil heater or a hot water heater, that unmet demand may be
met by the
employment of a supplemental heating device 112, such as may be an oil or gas
fired boiler.
In this embodiment supplemental heat, for defrost or such other purpose as may
be, in whole
or in part, may be employed in the event that refrigeration apparatus 20 is
not in service, and
an alternate heat source is required. To that end, pumps may urge coolant from
thermal
storage reservoir outlet manifold 73 to the boiler. In the event that extra
heating is not
required, the coolant may pass through the supplemental heating device, or
through a bypass,
without the heating element being in operation. After leaving the supplemental
heating
device, the fluid medium, having had a temperature boost (or not, as may be
appropriate in
the circumstances), may be directed to a pump such as may be used to urge the
warmed
coolant through the building fan coil forced air heating system, such as may
be used in the
facility, offices, and so on. At some times of year this system may be used to
provide heating,
and at other times of year to provide cooling (e.g. to act as an air
conditioner), such as when
coolant from ice builder 102 is directed through cooling circuit of apparatus
50 and the
building fan coil and returned. When used for heating, coolant in apparatus 70
exiting the fan
coil heating system is carried along return line to the inlet manifold.
Alternatively, or additionally, warm coolant leaving the supplemental heating
device
may be directed through building radiant zone heating apparatus such as may be
installed in
the various rooms of the facility.
Operation of apparatus 20 is governed by an electronic control system, such as
may
be termed energy management system 110, that includes a controller, and an
array of sensors
such as may include (a) temperature sensors; (b) pressure sensors; (c)
humidity sensors; (d)
volumetric flow rate sensors; (e) thermostat settings; (f) external ambient
condition sensors
(g) solar sensors; and (h) a clock, or clocks. The use of temperature and
pressure sensors in
refrigeration apparatus permits the operating statepoints to be known, and
adjusted,
according to existing heating and cooling demands, and according to
anticipated demand
such as may be determined from historic demand parameters stored in memory,
and on the
basis of external weather conditions.
CA 02809648 2013-03-15
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The electronic control system may include a memory having climatic data for
the site
of installation, including sun rise and sunset times for the location, and it
may have stored
ambient temperature and pressure information from recent days for use in
extrapolating
thermal load management estimates. It may include setting temperatures for the
various heat
sinks and heat sources. The memory data may include data for working fluid
pressure,
temperature, enthalpy, entropy, and density, from which other, intermediate
statepoint
conditions may be interpolated. The electronic control system may also include
programmed
steps for calculating the statepoints at which refrigeration apparatus 20
might best operate for
given loading conditions, or expected loading conditions based on time of day,
weather, and
historic demand.
The electronic controller may assess heating and cooling loads throughout the
facility.
Having done so, it may determine the output heat rejection temperature at the
thermal storage
reservoir, and may signal the various heat load pumps to operate as may be
required. Where
there is surplus heat rejection, the controller may cause the closed circuit
cooler to operate to
soak up the extra rejected heat. Where there is insufficient rejected heat to
meet the heating
load demand, the controller may cause the supplemental heating element to
operate to boost
the temperatures in the heating system or systems. Where a larger amount of
rejected heat is
desired, and before causing the supplemental heating element to operate, the
controller may
poll the condition of ice builder, may check against values stored in memory
for expected
heating demand, and may, if the ice builder is not fully charged (that is, it
is not at or below
its low set point temperature, and not at the minimum temperature that can be
achieve by
refrigeration apparatus 20). Provided that the time of day, and the point in
the expected load
cycle is appropriate, the controller may then signal refrigeration apparatus
20 to maintain a
higher than otherwise high side pressure, with corresponding higher rejection
temperature, or
it may cause the compressor to run at a higher mass flow rate, while also
causing the heating
load pumps to operate at a higher flow rate, the net result being a greater
rate of heat transfer.
Adjustment of the expansion device nozzle may also permit a change in upstream
pressure to
be obtained. That is, where a specific thermal rejection temperature is
desired to achieve, for
example, an 80 - 95 F temperature in the radiant space heating apparatus, the
system may
operate both to increase massflow rate of the working fluid in the cooling
machine 22, but, in
addition, to choke the system to yield a higher pressure in condenser 76 to
give a
combination of higher temperature and higher mass flow rate. This may then be
accompanied
by direction of coolant from the hot side of evaporator 34 to ice builder 102.
In the event that
greater heating is required, the electronic controller may signal for
supplemental heat.
CA 02809648 2013-03-15
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Where ice builder 102 is used to provide cooling to the condenser side, the
freezing
point of the thermal storage medium may in some circumstances be in excess of
32 F., but
less than the desired heat rejection temperature of the condenser.
In an alternate embodiment, as shown in Figure 2, an alternate refrigeration
apparatus
is shown as 120. Apparatus 120 is substantially the same as apparatus 20, but
differs
therefrom in being a cascade system, rather than the volatile brine system of
apparatus 20.
That is, apparatus 120 has a first cooling cycle circuit 116, which includes
compressors 24,
26; condenser 28; pressure drop apparatus 30, and evaporator 34. Apparatus 120
also has a
second cooling circuit 118 or second cooling machine 122, which includes
compressors 124,
126; evaporator 34 serving as the condenser 128 of second cooling circuit 118;
a pressure
drop apparatus, such as a nozzle or valve 130; and a cooling load output 132,
namely that of
cooling or refrigeration load 40, and its evaporators 42, 44, 46. Second
cooling circuit 118
may also include a receiver 136 mounted downsteam of nozzle 130 and upstream
of load 40.
Second cooling circuit 118 may include a refrigerant pump 148 operable to draw
refrigerant
from receiver 136 and to urge that refrigerant to load 40 (or to ice builder
102, if used). The
return from load 40 is directed back into receiver 136. Compressors 124, 126
draw from the
vapour of receiver 136, and output compressed gas to condenser 128, and so on.
Thus
second cooling circuit 118 is cascaded from first cooling circuit 116 the
through the shared
heat exchange medium of evaporator 34 ¨ condenser 128, both of circuits 116
and 118
having their own respective compressor stages. The upper cascade cycle is
defined by a
system such as ammonia vapour cycle cooling machine 22, and the lower cascade
cycle is
defined by a system such as a CO2 cycle machine in second cooling circuit 118.
In a summary of one embodiment, an industrial refrigeration system includes an
ammonia vapour cycle machine as cooling machine 22. A pair of compressors 24,
26 feed a
heat exchanger, such as condenser 28, with the condensate being collected in a
high pressure
reservoir 36. Working fluid leaves the high pressure reservoir through an
expansion valve, or
nozzle 30, whence it passes into another heat exchanger 34 in which the
ammonia
evaporates. The evaporated ammonia then flows back to the compressors, and so
on.
The use of ammonia in a distribution system inside an enclosed building may
not be
desired. In the system illustrated there is a cooling array symbolised by
cooling loads 40,
which may be the cooling distribution system of a meat packing plant. It may
be a CO2
based array, in which CO2 at perhaps about 1000 psia (+ or - 100 psi) is
condensed to liquid
in the heat exchanger 34 that is cooled by the ammonia system. The liquefied
CO2 then
CA 02809648 2013-03-15
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flows through a check valve and into the distribution piping to cooling heat
exchanger array
cooling load elements 42, 44, 46. Flashed CO2 returns to the cascade heat
exchanger, where
it is once again cooler.
The system includes a heat rejection and recapture circuit, namely thermal
storage
reservoir 70. In the embodiment the heat recapture system is a glycol system.
In this system
heat rejected from the ammonia primary system is carried by the glycol from
the condenser
28, 76 to a reservoir identified as a thermal equalizer tank 72.
As may be appreciated, from time to time the distribution array frosts up. In
this
example, the evaporators each have a CO2 circuit and a glycol circuit. When
there is a need
to defrost the system, the flow of CO2 to the array is interrupted, and flow
of hot glycol from
the thermal equalizer is directed to the evaporators of the distribution
system instead. This
heats the evaporators, causing them to defrost.
In this embodiment, (a) the system uses three working fluids (NH3, CO2,
Glycol); (b)
two of the three fluids are two phase-change fluids; (c) The heat for defrost
is stored in a
reservoir; the heat for defrost is transported by a third fluid, namely the
glycol; (e) The heat
exchangers on the refrigeration array side have segregated flow circuits for
the CO2 and the
glycol. Alternatively an HFC fluid, such as Freon or an HCFC, could also be
used as one of
the three fluids.
What has been described above has been intended illustrative and non-limiting
and it
will be understood by persons skilled in the art that other variances and
modifications may be
made without departing from the scope of the disclosure as defined in the
claims appended
hereto. Various embodiments of the invention have been described in detail.
Since changes in
and or additions to the above-described best mode may be made without
departing from the
nature, spirit or scope of the invention, the invention is not to be limited
to those details but only
by a purposive construction of the appended claims as required by law.
